The black spot is the chick. I have had some with good veins at a certain day and others with not real good veins at the same day.
Also darker eggs are harder to tell. I always mark any eggs that are suspect, but leave them in. I candle again at 13 or 14 days and any that are sure bad then get tossed. I candle last before the go to the hatcher. If I am still unsure, I put it in the hatcher anyway as long as it is not oozing or anything.

No it doesn't necessarily mean they are no good. Most of us, I believe, wait till at least day 10 to toss, I wait till day 14 unless it is completely obvious. The black dot is most likely the chick, but it's OK if it wasn't moving in all, the little peep could have been sleeping!
I have 2 chicken eggs in my bator that are due to hatch next week, and I am still not sure if they are both viable. They had the veining thing going on as well, one real good, and one not so good. I will wait till day 18 to candle again, and then I will know if the one is good or not. If you are unsure when candling, mark the egg, or put it in a different part of bator, and the next time you candle, like day 10-14, you can double check it. If it doesn't look like it is growing, then you should toss. But definitely wait till at least day 10. You can leave them in there for a while, as long as they aren't stinky or weepy. Then you KNOW they are bad!!

I candled my eggs on day 7 and only saw movement in only 3 of 15. Yesterday was day 14 and I had movement in 10 of 15!! One was dark with an air cell and veining like the other 10, but with no movement. I kept that one in the incubator. 4 others were clearly not viable at that point. They were clear whereas the others were dark throughout at least 3/4 of the egg. Of those 4 three turned out to be infertile and one had a tiny embryo and umbilical cord (probably from day 2-3). So don't give up too soon. I was convinced I only had 3 viable eggs and was scared they wouldn't make it to day 14.